1. Field of the Invention
The present invention relates to a reversible thermosensitive recording medium including an electronic information recording module having an antenna circuit, and a method for producing the reversible thermosensitive recording medium.
2. Description of the Related Art
IC cards have been increasingly being used in various aspects from users' daily lives to business activities. Actually, they are used as various cards (e.g., cash cards, credit cards, prepaid cards and ETC cards (electronic toll collection system)); in transportation facilities (e.g., railways and buses); as affiliate cards for digital broadcasting, 3rd generation mobile phones, etc.; in library service counters; and as student ID cards, employee ID cards, basic resident register cards, etc. Meanwhile, the amount of IC cards disposed of has been being increasing in accordance with diversification of the current economic and social activities.
In view of this, there is a keen need to create a recycling society, where material consumption is reduced and less environmental load is given, by reconsidering the current economic societies and lifestyles involving mass production, mass consumption and mass disposal to promote effective utilization and recycling of materials.
As one promising measure, electronic information recording module-embedded reversible thermosensitive recording media, wherein the electronic information recording module includes an electronic information recording element (hereinafter may be referred to as an “IC chip”) and an antenna circuit, can be used for reducing the amount of products disposed of. This is because they can rewrite information stored in the IC chip and show information as a visible image on their surface.
Such electronic information recording module-embedded reversible thermosensitive recording media have been used in the manufacturing industry as instruction sheets such as operation sheets, parts management sheets and process management sheets. Actually, there is repeatedly performed a cycle including winding an instruction sheet around a rod-like part or inserting it into a card case, and rewriting the content of the instruction sheet.
When an image is formed on or erased from it, a heating device (e.g., thermal head, erase bar, erase roller and erase plate) of the printer is pressed against the instruction sheet. Thus, rewriting of the instruction sheet must be performed so as not to break the electronic information recording module and not to avoid outflow of an adhesive from an adhesion portion between the electronic information recording module and the reversible thermosensitive recording medium. Furthermore, desirably, the instruction sheet is flexible and shows a high-quality image.
Moreover, a tag may be bent when the tag placed on a table surface is picked up, and a tag is taken out from a tag holder in an outer frame on a box. Thus, an IC chip portion in the tag is demanded to have mechanical durability against bending. Additionally, a medium is made thinner and flexible so as to improve efficiency of operation, such as picking up the medium. Namely, when the tag is picked up by hands upon operation, it is demanded that the tag is easily handled by flexibly changing its shape without locally bending its shape and breaking.
Moreover, as the tag is fed to a printer for image formation and erasure immediately after being held, it is also demanded that the tag is recovered from a shape varied upon holding to a flat shape at high speed, so as to reduce feeding failure and jam caused by curling or surface waviness in the printer.
Moreover, it is demanded that a printer is filled with tags as many as possible so as to decrease the number of access to the printer and shorten operation time, to thereby decrease the number of operation in the field.
Furthermore, from the viewpoint of improvement of close-contact properties with a thermal head so as to obtain high quality image, it is important to make a medium thin and flexible.
Such electronic information recording module-embedded reversible thermosensitive recording media each include an IC chip having a relatively large convex shape, and an antenna circuit having a relatively small concavo-convex shape.
If the surface of the reversible thermosensitive recording medium has concavo-convex portions and unevenness, a thermal head insufficiently comes into contact with a surface of the reversible thermosensitive recording medium and thus, heat is not sufficiently conducted in the surface thereof due to the heat insulating effect of air. As a result, the reversible thermosensitive recording medium cannot be rapidly cooled, causing failure in color development (unprinted image portion etc.) and a desired color development cannot be obtained in a part which is hard to be rapidly cooled.
For example, conventionally as shown in FIG. 15 proposed are IC cards including, as an over sheet, a reversible thermosensitive recording sheet 114 having at least one reversible thermosensitive layer 114c containing an intrinsically colorless or light-colored leuco dye and a reversible color developer allowing the leuco dye to develop color through application of heat and to erase the developed color through next application of heat, and including, as the other over sheet (film base 111) in which an IC card having an IC chip module (electronic information recording element) 112 is embedded, wherein a core member 113 is formed between these two over sheets through injection molding so that these are thermally bonded via the core member 113 to each other (Japanese Patent Application Laid-Open (JP-A) Nos. 11-154210, 2000-94866, 2000-251042, 2001-63228 and 2002-103654).
In FIG. 15, 114a denotes a protective layer and 114b denotes an intermediate layer.
In the above-described IC cards, the IC chip module 112 is provided so as to face the reversible thermosensitive recording sheet 114 and thus, the reversible thermosensitive recording medium is ununiformly pressed due to the IC chip module 112, whereby concavo-convex portions are undesirably formed on the recording medium. The reversible thermosensitive recording medium having the concavo-convex portions cannot be uniformly heated using a heating device and thus, heat cannot be uniformly conducted in the reversible thermosensitive recording medium when image formation is performed. As a result, an uneven image is formed on the reversible thermosensitive recording medium. Also, when image erasure is performed, a heating device is ununiformly pressed against the reversible thermosensitive recording medium, leading to failure in image erasure. Furthermore, the reversible thermosensitive recording medium has, on the surface thereof, a convex portion corresponding to the IC chip module 112. As a result, a heating device is pressed via the reversible thermosensitive recording medium against the IC chip module 112, causing a problem in that the IC chip module 112 is damaged or peeled off from the reversible thermosensitive recording medium.
In view of this, for example, JP-A Nos. 11-91274, 11-59037, 11-85938, 2003-141486 and 2003-141494 discloses countermeasures against the above problems. IC chip module-embedded reversible thermosensitive recording media disclosed in these Patent Literatures, however, have low flexibility and high rigidity, i.e., large thickness and high hardness.
JP-A Nos. 2005-250578 and 2006-344207, therefore, disclose reversible thermosensitive recording media in which an IC chip module is provided on an IC chip substrate disposed over a reversible thermosensitive recording sheet so that the IC chip module does not face the reversible thermosensitive recording sheet.
However, on the surface of an electronic information recording module having an electronic information recording element, an antenna circuit and a conductive member (hereinafter the electronic information recording module may be referred to as an “inlet”), concavo-convex portions are formed not only by the electronic information recording element but also by the antenna circuit and the conductive member. In this antenna circuit, a conductive member connects a front face of the antenna circuit board, in which surface an antenna circuit is formed, to a back face thereof to form a jumping circuit. When these front and back faces are penetrated using a laser, etc. for conduction, so-called caulking portions are formed. These caulking portions and the conductive member formed on the back face form concavo-convex portions on the electronic information recording sheet. Thus, as described above, even if only the IC chip is provided on the IC chip substrate over the reversible thermosensitive recording sheet so that the IC chip does not face the recording sheet, concavo-convex portions are formed on the reversible thermosensitive recording sheet. In particular, JP-A No. 2006-344207 describes that an antenna circuit board has, on its back face, an electrically short-circuited jumper wire. However, also when the jumper wire is formed on the reversible thermosensitive recording sheet side, the reversible thermosensitive recording medium problematically involves failures in image formation and erasure.
In order to solve the above-described problems, the applicant of the present invention has previously filed JP-A Nos. 2008-162077 and 2008-229911. In these Patent Literatures, an electronic information recording element is housed in a through hole of a core sheet so as not to project the electronic information recording element from the sheet; and a surface of the reversible thermosensitive recording sheet, on which surface no reversible thermosensitive recording layer is provided, is made to face a surface of the electronic information recording sheet, on which surface none of an antenna circuit board, an electronic information recording element, antenna circuit and a conductive member is provided, to thereby reduce concavo-convex portions on the surface of the reversible thermosensitive cording medium.
However, the electronic information recording element projects into a through hole, so as to avoid forming a convex shape on the surface of the reversible thermosensitive recording medium due to the electronic information recording element portion. The minute concavo-convex portions, such as the antenna circuit on the electronic information recording sheet cause concavo-convex portions on the surface of the reversible thermosensitive recording medium when the medium is repeatedly used, leading to failure in color development.
In the reversible thermosensitive recording media having such a configuration, failure in image formation/erasure can be overcome when the transfer speed of a printer used is 2 IPS. However, when the reversible thermosensitive recording media undergo image erasure/formation at high speed (3 IPS or higher), a rewritten image cannot be improved in its qualities (i.e., involves image fading and incomplete erasure) in an area corresponding to the electronic information recording sheet (including areas each corresponding to an IC chip, an antenna circuit and a conductive member), leading to failure in color development.
Conventionally, the improvement in qualities has been achieved on a rewritten image area in an electronic information recording sheet at a transfer speed of 2 IPS. When image erasure and formation is performed at a transfer speed of 3 IPS, a rewritten image has not been improved in its qualities.
This is because the higher the transfer speed of the printer, the more difficult it is that heat applied from the erasure head of the printer is conducted in the reversible thermosensitive recording medium. In order to improve such state, when a temperature for image erasure is increased for improving erasability, the reversible thermosensitive recording medium is excessively heated by the erasure head. In this state, when image formation is performed, the reversible thermosensitive recording medium cannot be rapidly cooled to prevent color development (to be in an erasure mode). Consequently, when the electronic information recording module has, on a surface thereof, height differences and concavo-convex portions (i.e., the electronic information recording sheet does not have a flat surface and has concavo-convex portions in which the height from the top surface to the base portion is about 50 μm and which are formed by the IC chip, the antenna circuit, and the caulking portion connecting the antenna circuit to the IC chip), a thermal head insufficiently comes into contact with a surface of the reversible thermosensitive recording medium and thus, heat is not sufficiently conducted in the surface thereof due to the heat insulating effect of air. As a result, the reversible thermosensitive recording medium cannot be rapidly cooled, causing failure in color development.
Meanwhile, the reversible thermosensitive recording medium used in the field of logistics, and image erasure and formation at a high speed (a transfer speed used in a printer is 3 IPS or higher) is demanded for cost reduction such as shortening of an operation time.
Under such circumstances, demand has arisen for a high-quality electronic information recording element-embedded reversible thermosensitive recording medium in which, even when image erasure and formation is performed at a high speed of 3 IPS or higher, white voids and image fading do not occur in the formed image areas each corresponding to the surrounding area of the electronic information recording sheet, to the electronic information recording element, to the antenna circuit and to the conductive member; image erasure can be completely performed.
Moreover, it is demanded that a tag is easily handled by flexibly changing its shape without locally bending its shape and breaking according to the shape variation upon holding. Moreover, as the tag is fed to a printer for image formation and erasure immediately after being held, it is also demanded that the tag is recovered from a shape varied upon holding to a flat shape at high speed, so as to reduce feeding failure and jam caused by curling or surface waviness in the printer. Furthermore, when a large number of the reversible thermosensitive recording media are stacked and print at once, it is demanded that a printer is filled with tags as many as possible so as to decrease the number of access to the printer and shorten operation time, to thereby decrease the number of operation in the field.
Moreover, proposed is a reversible thermosensitive recording medium including a sheet having a through-hole into which an electronic information recording element is inserted, and a sheet having a hollowed-out portion for housing an electronic information recording sheet between a reversible thermosensitive recording sheet and a sheet facing a surface of the reversible thermosensitive recording sheet (see JP-A No. 2009-173013).
According to this proposal, the electronic information recording element is housed in the through-hole of the sheet so as not to project the electronic information recording element from the sheet and the electronic information recording sheet is housed in the hollowed-out portion of the sheet, so that the reversible thermosensitive recording medium can be made flat without forming unevenness and concavo-convex portions caused by an antenna circuit of the electronic information recording sheet, and thus an occurrence of an unprinted image portion can be reduced to some extend.
However, as sheets for respectively compensating for the unevenness of the electronic information recording element and concavo-convex portions of the antenna circuit are provided inside of the medium, the reversible thermosensitive recording medium becomes thicker, adversely affecting flexibility.
As a proposal for a module for an IC card, such structure is proposed that the module has a substrate and an IC chip mounted on the substrate, wherein a protective member for covering the IC chip is bonded to the substrate, and between the protective member and the IC chip a gap is formed to prevent the protective member from directly contacting with the IC chip. Moreover, the protective member is a plate-shaped or sheet-shaped protective cap having a concave portion on its surface, in which the IC chip is housed with a gap left between them (see JP-A No. 11-11060).
However, in this case, concavo-convex portions of the antenna circuit in the electronic information recording sheet is not considered. If this structure is employed in a reversible thermosensitive recording medium for repetitive image formation and erasure, the concavo-convex portions may be formed on a surface of the reversible thermosensitive recording medium, causing failure in color development.